Aluminium Slab: High-Integrity Cast Slab for Rolling, Forging & Machining

What aluminium slab is and who buys it

Slab, also called rolling ingot, sheet ingot or flat ingot, is the starting point for rolled aluminium. Molten metal of a controlled composition is cast vertically into a water-cooled rectangular mould; as the solid shell forms, the starter block descends and water sprays directly onto the emerging ingot. The result is a rectangular slab several metres long with a fine, relatively uniform cast structure.

Three groups of buyers use slab. Rolling mills hot roll it into plate, sheet and coil. Forging shops use sections of thick slab as stock for open-die and closed-die forgings, especially in 2xxx and 7xxx alloys where large cross-sections are needed. Machining and mould makers buy sawn slab blocks when they need a section thicker than rolled plate can provide, or when they accept cast properties in exchange for size.

For standard sheet and plate production the commercial specification of a rolling slab is well established; our rolling slab and sheet ingot specification guide covers that side. This page focuses on high-integrity slab: material for high-strength alloys, thick plate, forgings and fatigue-critical parts, where internal soundness and traceability matter as much as chemistry.

Slab alloys and what each is used for

High-strength 7xxx and 2xxx alloys are the most demanding to cast. 7050 and 7075 have a long freezing range and contract strongly, so they are prone to hot tearing during solidification and to cold cracking from thermal stress after casting. Large 7xxx slabs are therefore cast at controlled speeds, often stress-relieved or homogenised promptly after casting, and inspected more thoroughly than 5xxx or 6xxx slabs.

High-magnesium 5xxx alloys such as 5083 oxidise readily in the melt, so melt cleanliness and filtration matter. 4032 and 2618 are often used as forging stock, where a fine, uniform cast structure improves forgeability and final properties.

From melt to slab: the steps that decide internal quality

1. Melting and alloyingPrimary metal, master alloys and controlled scrap are melted and adjusted to the target analysis, usually aimed well inside the standard limits so that properties are consistent.
2. Melt treatmentThe melt is fluxed and degassed (often by inline rotary degassing with argon or argon-chlorine mixtures) to remove hydrogen, which otherwise forms porosity, and alkali impurities.
3. FiltrationCeramic foam or deep-bed filters remove oxide films and inclusions. Two-stage filtration is common for aerospace and high-integrity slab.
4. Grain refinementAn Al-Ti-B or Al-Ti-C grain refiner is added inline to give fine, equiaxed grains and reduce hot-tearing susceptibility.
5. DC castingMetal is cast into a water-cooled mould at a controlled speed and temperature. Start-up and end of cast are the most defect-prone phases, so butt and head ends are cut off.
6. HomogenisationThe slab is soaked at high temperature for many hours to even out microsegregation, dissolve coarse constituents and precipitate dispersoids that control grain structure later.
7. Scalping and sawingThe rolling faces are milled to remove the cast surface layer, which carries segregation and oxides. Ends are sawn square; slabs for forging or machining are cut into blocks.
8. Inspection and releaseChemistry, dimensions, surface and, where required, ultrasonic, macro-etch and grain size tests are completed before the slab is released with its traceability records.

Casting defects that matter, and how they are controlled

No single test finds all of these. Chemistry confirms the alloy and impurity levels, ultrasonic testing finds internal voids, cracks and large inclusions, macro-etching of a cross-section reveals grain structure and segregation patterns, and metallographic sections show porosity and constituent particle size. High-integrity orders typically combine several of them.

What to specify for inspection and traceability

State the inspection plan in the enquiry. Testing adds cost and time, and the right level depends on the downstream product: commercial sheet ingot needs much less than slab destined for aerospace plate or forgings.

Typical slab sizes and weights

Slab weight is volume multiplied by density. The table gives calculated weights for common cross-sections at three densities: 2.70 g/cm³ (6xxx), 2.66 g/cm³ (5083) and 2.81 g/cm³ (7075). For 7050 use about 2.83 and for 2014 about 2.80.

These weights explain why slab logistics need planning. A single large slab can weigh well over ten tonnes, so lifting equipment, container or breakbulk shipment and lashing must be agreed in advance. Sawn blocks for forging or machining are much easier to handle and ship.

Slab compared with billet, remelt ingot, block and plate

A useful rule: if your part fits within the thickness of available rolled plate or a forged block, those wrought products offer better and more consistent properties than cast slab, because hot working closes porosity and breaks up the cast structure. Choose sawn slab when the section is larger than plate or forgings allow, or when the part is lightly stressed and the lower cost of cast material is attractive.

How to order aluminium slab from Metline

1. Define the useTell us whether the slab is for rolling, forging or machining, and the final product. This sets the inspection level and condition.
2. SpecifyAlloy and standard (Aluminum Association, EN 573-3 or GB/T 3190), any tighter composition limits, dimensions or cut lengths, and quantity.
3. Agree inspectionChemistry, UT class, macro-etch, grain size, porosity checks and documentation.
4. QuoteWe confirm availability, condition (as cast, homogenised, scalped or sawn), certification and delivery terms (EXW, FOB, CIF or DAP).
5. ShipSlabs and blocks are marked with cast numbers, protected and secured for breakbulk or container shipment worldwide.

Related cast and wrought products

Aluminium (aluminum) slab: frequently asked questions